Exhaust gas emitted from an internal combustion engine, particularly a diesel engine, is a heterogeneous mixture that contains gaseous emissions such as, but not limited to, carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NOx”), as well as condensed phase materials (liquids and solids) that constitute particulate matter (“PM”). Catalyst compositions, typically disposed on catalyst supports or substrates, are provided in an engine exhaust system as part of an aftertreatment system to convert certain, or all of these exhaust constituents into non-regulated exhaust gas components.
One type of exhaust treatment technology for reducing emissions is a particulate filter (“PF”). The PF is designed to remove diesel particulate matter, or soot, from exhaust gas of an engine. The particulate matter removed from the exhaust is entrapped by, and entrained in, the PF. When accumulated soot reaches a predetermined level the PF is either replaced or regenerated. Replacement or regeneration facilitates that soot removal continues at desired parameters.
Many engines include a controller having a soot out model that predicts soot accumulation in the PF. The soot out monitor employs various engine operating parameters to predict soot accumulation levels in the PF. The operating parameters include duration and number of accelerations, duration of operation at constant RPM above idle, and idle time. Inaccurate soot accumulation predictions could lead to premature replacement or cleaning of a PF, or operating conditions in which soot is not removed at desired levels. Prediction inaccuracies tend to occur after prolonged periods of low speed operation. During lower speeds, accurate pressure change readings are difficult to obtain. Once normal highway speed is resumed, the controller may sense a sudden increase in a rate of soot accumulation. The sudden change in soot accumulation could cause the controller to force the engine into a reduced power mode which necessitates maintenance. Accordingly, it is desirable to provide a soot out model with the flexibility to adjust soot accumulation rates following low speed and idle operations.